Metal working processes of many kinds are used in the fabrication of metal goods. Typically metal is removed from the workpiece during metal working. Examples of metal working processes include machining, cutting, drilling, grinding, turning, milling, tapping and broaching. Metal working differs from metal forming. In metal forming typically no metal is removed. Examples of metal forming processes include rolling, forging, molding, stamping, casting, ironing, drawing, and extruding. In metal forming operations, the metal is typically preheated to at least about 800.degree. C. so that the metal can be more easily formed into the desired shape. In metal working operations, the metal is typically not preheated; the only heat incident to the operation is that caused by the metal working operation itself.
In all metal working operations it is necessary to lubricate the interface between the workpiece and the tool to decrease the force required to work the metal; to cool the workpiece; to remove chips from the cutting zone; to impart a good surface finish; and to extend the life of the tool. The formulation of lubricant compositions is complex, because a wide variety of compounds may be used, as, for example, antifriction agents, anticorrosion agents, surfactants, and biocides.
Triaryl phosphate esters have been proposed for use in metal working lubricant compositions. Berens, U.S. Pat. No. 4,362,634, discloses metal working lubricant compositions that comprise a polyol ester, such as a pentaerythritol/fatty ester, as the major ingredient together with a triaryl phosphate ester and a carboxylic ester non-ionic surfactant of the anhydrosorbitol or glycerol ester type, such as sorbitan monotallate. The phosphate ester comprises 1 to 10 weight % of the concentrated lubricant composition. About 2 to 30 weight % of concentrated composition can be dispersed with water to form a diluted lubricant composition as an emulsion that was reported to be phase stable for at least one hour under quiescent conditions.
Metal working lubricant compositions are preferably produced as concentrates, which are diluted prior to use. Concentrated lubricant compositions are prepared by the manufacturer and shipped in drums to the user, who may store the drums of concentrated lubricant composition for several weeks to months prior to use. Because the lubricant properties of the metal working lubricant composition are typically lost if the lubricant composition deemulisifies, the concentrated lubricant composition should have a shelf life (stability, i.e., time before deemulsification occurs) at room temperature (about 25.degree. C.) of at least one month, and preferably at least six months. The high temperature (about 75.degree. C.) stability and the low temperature stability (about -15.degree. C.) should each be at least 5 days. Following dilution of the concentrated lubricant composition, the resulting diluted lubricant composition should have a shelf life at room temperature of at least one month, preferably at least six months, a high temperature stability of at least one day and a low temperature stability of at least one day.
Thus, there is a need in the art for both concentrated and diluted metal working lubricant emulsions that are stable for longer periods so that they can be produced and stored for longer periods of time prior use.